Project Summary Novel treatments are desperately needed by patients with Becker muscular dystrophy (BMD), and anti- inflammatory therapies hold great promise for treating patients with this condition. However, the slow progressive nature of the disease, small numbers of patients, variable onset and clinical presentation, and lack of biomarkers presents a serious barrier to drug development in BMD. A first-in-class steroid, vamorolone, has shown promise for the treatment of young boys with Duchenne muscular dystrophy and is in a randomized, blinded and controlled, confirmatory study for this indication. In this project, we propose a 24-week pilot trial of vamorolone 6 mg/kg/day in 30 ambulatory patients with BMD at 2 sites, evaluating safety and tolerability. Biomarkers, creatine kinase, macrophage derived chemokine, and microRNA 146a, and the timed 10 meter run/walk test will also be evaluated throughout the trial, to assess the usefulness of these potential treatment responsive biomarkers to this anti-inflammatory drug in BMD patients. If vamorolone is demonstrated to be safe and tolerable in this study, a controlled study of vamorolone treatment for BMD patients will be planned. Evaluation of pharmacodynamic biomarkers in this short trial serves to provide objective evidence for drug mechanism of action; if there is expected change in this pilot trial, these biomarkers would be further studied in the next phase trial.